1. Field of the Invention
This invention relates to an apparatus for providing visual indicia of the safe operating range of the interrupter assembly of a circuit breaker interrupter apparatus.
2. Background Information and Description of the Prior Art
Circuit breakers provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and low level voltage conditions. Typically, circuit breakers include a spring-powered operating mechanism which opens electrical contacts to interrupt the current through the conductors on an electrical system in response to abnormal conditions. In particular, vacuum circuit interrupter apparatus have been known which include separable main contacts disposed within an insulating housing. Generally, one of the contacts is fixed relative to both the housing and to an external electrical conductor which is interconnected with the circuit to be controlled by the circuit interrupter. The other contact is movable. In the case of a vacuum circuit interrupter, the movable contact assembly usually comprises a stem of circular cross section having the contact at one end thereof enclosed within the vacuum chamber and a driving mechanism at the other end which is external to the vacuum chamber. An operating rod assembly is provided which carries a rotatable contact bell crank which is slidable on the operating rod and rotates about a pivot pin upon motion of the operating rod. This plate is connected to the stem of the movable contact. Motion of the plate causes motion of the movable contact into or out of engagement with the fixed contact.
The operating rod assembly is operatively connected to a latchable operating mechanism which is responsive to current. When an abnormal condition is reached, the latchable operating mechanism becomes unlatched which causes the operating rod to move to the open position. The motion of the operating rod, in turn, causes the contact bell crank to rotate and, as discussed above, this controls motion of the movable contact.
Compression springs are provided in the operating rod assembly in order to be able to separate the movable contact from the fixed contact and to assure the necessary force so that the contacts will not accidentally open in inappropriate conditions. In addition, when appropriate circumstances requiring interruption of the circuit do arise, an adequate force is needed to open the contacts with sufficient speed. If the contacts do not open quickly, there is a risk of the contacts welding together and failure to interrupt the current.
If, on the other hand, a low level fault occurs, the current level is not high so the contacts would not weld, however, due to inadequate opening energy the breaker may open but it may continue to conduct.
In order to achieve the adequate interrupt speed and force, springs are mounted on the operating rod assembly. The springs are typically mounted towards one end of the operating rod on what is referred to as the contact wipe portion of the operating rod assembly. Contact wipe is a measure of the force required to hold the vacuum interrupter contacts closed and the energy to force the contacts open with sufficient speed for safe and clean interruption as discussed above. As noted above, the contact springs which comprise part of the contact wipe assembly must provide the force to hold the contacts closed and the energy to pry them open with appropriate speed. Therefore, if such springs are compression springs as is typically the case, it is important that the springs have sufficient compression during operation. On the other hand, if tension springs are utilized, adequate tension must exist.
In a typical case, the spring is held on the operating rod between a disk-shaped spacer member which is carried along the operating rod and a shoulder portion of a set of contact wipe plates which are mounted at one end of the operating rod and spaced apart from the spacer member. When the contacts are closed, the operating rod travels toward its closed position. The contact wipe plates are slidably mounted on the operating rod at the same point at which the rotatable contact bell crank is mounted. When the contacts seat, motion of the contact wipe plates stop. However, motion of the operating rod continues until it travels to its full extended position. At this point, the spring is fully compressed between the spacer member and the shoulder section of the contact wipe plates.
At present, there is not a known method of visually checking (without measurements) the spring compression (or tension) to determine whether it is adequate. Adequate spring compression is, in one respect, an indication of the contacts being in good condition. This is because contacts which are worn would require a greater degree of travel by the contact wipe plates which would mean that the compression of the spring between the shoulder portion of the contact wipe plates and the disk-shaped spacer would not be as great.
There is a need, therefore, for a convenient and easy to use inspection apparatus for use with the contact wipe springs with which the compression of the springs may be visually inspected. This would serve as an indication of correct contact force and indirectly provides an indication of the integrity of the contacts. There is a preferred need for such a device which does not require additional measuring apparatus and does not require disassembly of the circuit breaker or any portion of it.